1. Field
The present invention relates to wireless communication, and more particularly, to an apparatus and method for transmitting information about power headroom in a multiple component carrier system.
2. Discussion of the Background
A wireless communication system uses one bandwidth for data transmission. For example, the 2nd generation wireless communication system uses a bandwidth of 200 KHz to 1.25 MHz, and the 3rd generation wireless communication system uses a bandwidth of 5 MHz to 10 MHz. In order to support an increasing transmission capacity, the bandwidth of a recent 3GPP LTE or 802.16m has extended to 20 MHz or higher. To increase the bandwidth may be considered to be indispensable so as to increase the transmission capacity, but to support a high bandwidth even when the quality of service required is low may generate great power consumption.
In order to solve the problem, there has emerged a multiple component carrier system in which a component carrier having one bandwidth and the center frequency is defined and data is transmitted or received through a plurality of component carriers using a wide band. That is, a narrow band and a wide band are supported at the same time by using one or more component carriers. For example, if one component carrier corresponds to a bandwidth of 5 MHz, a maximum 20 MHz bandwidth can be supported by using four component carriers.
A method of an eNodeB efficiently using the resources of a user equipment is to use power headroom information provided by the user equipment. The power headroom information is essential information for efficiently allocating uplink resources in wireless communication and reducing the battery consumption of a user equipment. When the user equipment provides the power headroom information to the eNodeB, the eNodeB can estimate maximum transmission power in uplink that the user equipment can withstand. Accordingly, the eNodeB can perform uplink scheduling within a range in which the estimated maximum transmission power in uplink is not exceed.
Power headroom for each component carrier has a relatively small variance. Meanwhile, when a plurality of component carriers is dynamically scheduled, the variance may become relatively high. For this reason, the power headrooms of component carriers must be taken into account individually or overall. In this case, there are problems in that to control the power of a user equipment becomes more complicated and the amount of control information occupied by a Power Headroom Report (PHR) is increased. However, a method of reporting power headroom with consideration taken of a plurality of dynamically scheduled component carriers or the structure of a message for a PHR has not yet been defined.